Alex Jones, whose InfoWars website is viewed by millions, says that the 2012 Sandy Hook massacre was an elaborate hoax invented by government-backed “gun grabbers.”CreditCreditIlana Panich-Linsman for The New York Times

WASHINGTON — After the body of Jesse Lewis, age 6, was recovered from his classroom at Sandy Hook Elementary School, his father, Neil Heslin, cradled him for a final time. At the top of Jesse’s forehead was the gunshot wound that ended his life. “It meant a lot to be able to see him,” Mr. Heslin said in an interview. “When he was born, I was the first to see him, and I was the last one to hold him.”

Alex Jones, an online conspiracy theorist whose InfoWars website is viewed by millions, seized on this agonizing recollection to repeat the bizarre falsehood that the 2012 shooting that killed 20 first graders and six adults at the elementary school in Newtown, Conn., was an elaborate hoax invented by government-backed “gun grabbers.”

On his radio show, Mr. Jones said Mr. Heslin needed to clarify “because the coroner said no, the parents weren’t allowed to have touched the kids or have seen the kids.” He played a video in which the InfoWars “reporter” Owen Shroyer says of Mr. Heslin, “He’s claiming that he held his son and saw the bullet hole in his head.”

“That is not possible,” Mr. Shroyer said.

More than five years after one of the most horrific mass shootings in modern history, the families of Sandy Hook victims are still enduring daily threats and online abuse from people who believe bogus theories spread by Mr. Jones, whom President Trump has praised for his “amazing” reputation.

Now, for the first time, the families are confronting Mr. Jones in court.

“When anybody’s behind a machine, whether it’s a gun or a computer or a car, a dehumanization takes place that makes it easier to commit an act of violence,” Veronique De La Rosa, the mother of Noah Pozner, another victim, said in an interview. She is suing Mr. Jones, she said, because she wants to force him to admit to his devotees that “he peddled a falsehood, that Sandy Hook is real and that Noah was a real, living, breathing little boy who deserved to live out the rest of his life.”

In three separate lawsuits — the most recent was filed on Wednesday in Superior Court in Bridgeport, Conn. — the families of eight Sandy Hook victims as well as an F.B.I. agent who responded to the shooting seek damages for defamation. The families allege in one suit, filed by Koskoff, Koskoff & Bieder in Bridgeport, that Mr. Jones and his colleagues “persistently perpetuated a monstrous, unspeakable lie: that the Sandy Hook shooting was staged, and that the families who lost loved ones that day are actors who faked their relatives’ deaths.”

More broadly, the families are seeking society’s verdict on “post truth” culture in which widely disseminated lies damage lives and destroy reputations, yet those who spread them are seldom held accountable. The suit filed on Wednesday emphasizes Mr. Jones’s reach and connection to Mr. Trump. On his show last year, Mr. Jones called himself and his listeners “the operating system of Trump.” Later he said, “I’m making it safe for everybody else to speak out just like Trump’s doing, on a much bigger scale.”

When the president called the news media the “enemy of the people” last year, Mr. Jones proudly tweeted that he used the phrase first, in 2015.

Mr. Trump has also echoed InfoWars’ false claims that Hillary Clinton benefited from the votes of millions of illegal immigrants in the election, and repeated InfoWars’ bogus charge that the news media covers up terrorist attacks.

Fantastical explanations for traumatic events punctuate history. But 21st-century conspiracy theorists gather in vast online networks where bogus claims reach millions in minutes, and where participants like Mr. Jones use social media and online marketing to turn an eccentric preoccupation into a thriving commercial enterprise.

Mr. Jones pitches the false claims, along with diet supplements and survivalist gear, on his InfoWars website, radio program and YouTube channel. His videos have been viewed more than a billion times. He most likely sells $7 million to $12 million worth of diet supplements a year, according to an analysis in New York magazine.

Sandy Hook families have been followed, videotaped and harassed by people demanding “proof” that their loved ones died. Monuments to the slain children in Newtown have been stolen and defaced. An Alex Jones devotee went to prison last year after phoning and emailing Leonard Pozner, Noah’s father, with death threats, including “LOOK BEHIND YOU IT IS DEATH.” The family relocated to a gated community with 24-hour security. Their daughters, who survived the shooting, check doors and windows before going to bed, and sleep with the lights on.

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Parents of some of the Sandy Hook victims and one of their lawyers in November outside the Connecticut Supreme Court, where a hearing was held on their attempt to sue the maker of the gun used in the shooting.CreditJessica Hill for The New York Times

Nate Wheeler, 15, who hid in a school supply closet during the shooting that killed his 6-year-old brother, Ben, struggles to understand false online claims that both boys and their parents were “crisis actors” and that his brother never died, his father, David Wheeler, said in an interview. Mr. Wheeler has found messages on his social media accounts telling him that he will face divine judgment for lying when he dies, he said.

Wednesday’s suit follows twin defamation lawsuits filed in Texas in April by the parents of two other victims — Mr. Heslin, and Ms. De La Rosa and Mr. Pozner. Mr. Jones did not respond to requests for comment. After the Texas lawsuits were filed last month, he posted a 10-minute videotaped response suggestive of how his positions onthe event shifted. “I questioned the P.R. and the talking points that surrounded the Sandy Hook massacre,” he said. “But very quickly I began to believe that the massacre happened, despite the fact that the public doubted it.”

And yet in an earlier video on his website, titled “Alex Jones Final Statement on Sandy Hook,” he says: “If children were lost in Sandy Hook, my heart goes out to each and every one of those parents, and the people that say they’re parents that I see on the news. The only problem is, I’ve watched a lot of soap operas, and I’ve seen actors before.”

Mr. Jones claims First Amendment protection for his endeavors, but the lawsuits challenge that defense. “The First Amendment has never protected demonstrably false, malicious statements like the defendants’,” the suit filed on Wednesday says, referencing New York Times Company v. Sullivan, the Supreme Court case upholding freedom of the press.

Defamation cases are difficult to win. Lawyers for the victims’ families “will have to show that the statements were false statements of fact, not opinion, and that Alex Jones was at least negligent, and did not take the steps an ordinary reporter would take to corroborate facts,” said David Snyder, executive director of the First Amendment Coalition, a free-speech advocacy group. The legal burden on the families will be heavier yet if they are deemed to be public figures.

Mr. Jones, 44, grew up in the Dallas suburb of Rockwall, the son of a dentist and a homemaker. He told an interviewer in 2011 that he was profoundly shaped by reading his father’s copy of “None Dare Call It Conspiracy,” a 1971 best-seller by Gary Allen, a John Birch Society spokesman and speechwriter for George Wallace, the former Alabama governor, during his presidential run.

Mr. Jones got his media start as a community college student in Austin in the early 1990s, when he repeatedly insisted on community access cable that the government was behind the 1995 bombing of the federal building in Oklahoma City. Distracted by his mission to warn of the dangers of the American government, Mr. Jones dropped out of college and founded InfoWars in 1999, in time to call the Sept. 11 terrorist attacks an “inside job.”

Mr. Jones might have remained a peripheral conspiracy theorist had it not been for Mr. Trump, who appeared on Mr. Jones’s radio show during the 2016 campaign, pledging, “I will never let you down” and “we’ll be speaking a lot.” Mr. Jones’s following surged.

The Texas suits focus on Mr. Jones’s comments over the previous year, including a segment on his radio show last year titled “Sandy Hook Vampires Exposed.” Mark Bankston, a partner in the Houston law firm Farrar & Ball, who is leading the team representing Mr. Heslin, Mr. Pozner and Ms. De La Rosa, said the firm’s young lawyers grew up listening to Mr. Jones’s radio show, and found him an amusing, if weird, local character.

But now Mr. Bankston has a different perspective. “For Alex Jones, it appears that the only real thing on his mind is his business,” Mr. Bankston said. “And if you threatened that, you can make him understand that these kinds of practices have a cost. And if that message goes out to others like him, that’s a victory for these families.”

Mr. Jones exhorts his followers to investigate what they call “false flags,” events concocted by the government or other powerful entities determined to usurp citizens’ rights. Mr. Jones issued a rare apology last year after spreading a fake story that Mrs. Clinton and Democratic operatives were running a child pornography ring inside a Washington pizzeria, which had led Edgar M. Welch, a Jones listener, to enter the pizzeria in 2016 with an assault-style rifle, firing it. No one was hurt, and Mr. Welch is now serving a four-year prison term.

Last year, InfoWars posted a video on its website with the headline “Idaho Yogurt Maker Caught Importing Migrant Rapists,” falsely claiming that a Chobani factory in Twin Falls, Idaho, that employs refugees was connected to the 2016 sexual assault of a child. The charges fueled an uproar in the town, and Chobani sued Mr. Jones. As part of a settlement, Mr. Jones admitted on his radio show that he had “mischaracterized” Chobani, and retracted the false material.

Mr. Wheeler has a theater background, and Sandy Hook deniers have, among other things, posted a photo of him at the school alongside one of William Aldenberg, an F.B.I. special agent who responded to the shooting and is a party to the lawsuit. The deniers say that Mr. Wheeler is an actor playing both “roles.”

Scott Shane contributed reporting.

A version of this article appears in print on , on Page A1 of the New York edition with the headline: Sandy Hook Suits Target Fabulist And Online ‘Post Truth’ Culture. Order Reprints | Today’s Paper | Subscribe